Carrier-concentation-dependent electron–LO-phonon coupling observed in GaAs-(Ga,Al)As heterojunctions by resonant-polaron cyclotron resonance

Abstract

The cyclotron resonance (CR) of the two-dimensional electron gas (2D EG) in GaAs-(Ga, A1)As heterojunctions has been studied in the resonant-polaron regime for 2D carrier densities N, in the range (0.8-5.4) && 10" cm . A reflectivity technique has allowed the CR to be recorded at energies up to 35.63 meV, within the GaAs reststrahlen band, and a calculation of the dielectric response of the complete heterostructure has enabled the effective masses to be reliably evaluated from the line shapes and positions of the resonances. The results indicate that the 2D electrons are coupling to the LO phonon (36.7 meV), in agreement with theoretical predictions. At low carrier densities, the resonant-polaron contribution to the effective mass becomes apparent at cyclotron energies above 25 meV, and increases in size as the LO-phonon energy is approached: however" this mass enhancement is removed rapidly as N, is increased, indicating the importance of Landau-level occupancy and screening in the 2D EG. Close to the LO-phonon energy, large shifts in the resonance position, which are several times the linewidth in size, are produced by varying N, . This large N, dependence explains previous convicting reports of "enhanced" or "reduced" polaron effects in the 2D electron gas. A comparison of the experimental results with existing memory-function calculations of the polaron contribution to the effective mass indicates that the greater part of the N, dependence can be ascribed to Landau-level occupancy effects.

Magnetopolaron effect on shallow indium donors in CdTe

“…This leads to a resonant splitting of this transition, the so-called resonant polaron effect, which has been studied for several decades in bulk semiconductors 2,3 and more recently in low-dimensional systems. [4][5][6] Most of the studies reported so far have focused on weakly polar materials, such as InSb ͑Fröhlich constant ␣Ϸ0.02) or GaAs (␣Ϸ0.07). In such materials, the polaron splitting is small ͑of the order ␣ 2/3 ប LO , see Ref.…”

Energy-Band Structure: Electron and Hole Effective Masses

“…65,67,69,70,8 ' 1 Cyclotron-resonance measurements was also reported for wide (0.1 -0.3 um) modulation-doped Al^Ga^As graded parabolic quantum wells for electron areal densities n s =10 9 -2.5x10" cm" 2 . 75 A clear dependence of the cyclotron frequency on n, was observed in the extreme quantum limit which was understood in terms of alloy effects.…”

Cyclotron resonance and spin states in GaAs/Ga1−xAlMichels1, Daly2, Gee3 et al. 1996Phys. Rev. BSelf Cite11020View full textAdd to dashboardCite

“…where K 2 is a parameter describing the slope of the effective mass when plotted as a function of energy, m 0 is the band edge effective mass, ͗T z ͘ is the kinetic energy due to the shape of the 2DES confinement potential, E g the GaAs band gap, and E CR ϭប c Ϯg* B B the cyclotron energy. [26][27][28][29] The splitting has a characteristic B 2 dependence because the magnetic field enters both the cyclotron separation between the Landau levels and the g factor difference between the ground and first Landau level. 26,27 If the electrons do not interact and behave as a classical gas of single particles, the CR spectrum of a 2DES should be identical to that found in high-purity, low carrier concentration bulk GaAs.…”